Poor recording detection device and image recording apparatus using the same

ABSTRACT

A poor recording detection device includes an illumination unit which applies illumination light to a recording medium after recording on the recording medium and a camera unit which picks up an image recorded on the recording medium to which the illumination light is applied and outputs detected information. A poor recording determination unit outputs reference detection information obtained by detecting a reference recording image by the camera unit after recording the reference recording data on the recording medium as input recording data, generates correction information by comparing the reference detection information with the reference recording data and generates corrected input recording data obtained by correcting the input recording data on the basis of the correction information, and detects a poor recording by comparing the input recording image information and the corrected input recording data after recording the input recording data on the recording medium.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application Nos.2006-341830 filed on Dec. 19, 2006 and 2007-264884 filed on Oct. 10,2007, which is incorporated hereinto by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image recording apparatus forrecording images by fusing ink or the like into a recording medium, suchas paper, film or the like, and more particularly to a poor recordingdetection device for detecting poor recording when recording data on arecording medium by the recording head of an image recording apparatusand an image recording apparatus using it.

2. Description of the Related Art

Some image recording apparatus for recording images by fusing ink into arecording medium, such as a large amount of papers, films or the likerecords an image while carrying the recording medium at a high speed ofseveral tens˜several hundreds m/min. In such high-speed image recordingit is impossible to visually check whether image data transmitted from ahigher-level device coincides with a recorded image by human eyes. Evenin low-speed image recording, sometimes visual check by human eyes lacksaccuracy. Therefore, in such an image recording apparatus a technologyfor electronically reading a recorded image and detecting poor recordingby comparing this image with an image represented by image datatransmitted from a higher-level device dot by dot is proposed.

For example, Japanese Patent Application No. 2003-54095 discloses aninvention whose object is to make an accurate inspection by reading theprinting image of a printing matter and enabling it to appropriatelycorrespond to image data by correcting its skew by a simple method whenchecking a printed result by matching it with its original printingimage data. It checks the printed result by attaching a reference lineto inputted printing image data by a reference mark attachment unit andprinting it, reading printed image read by a scanner unit for each lineby a position correction unit, sliding and correcting the data for eachline in such a way that the utmost-left dot may be positioned in thereference line attached by the reference attachment unit and collatingit with the original printing image data.

Japanese Patent Application No. H7-89063 discloses an invention whoseobject is to enable the detection of a very small defect in a printingmatter inspection system by aligning the printing matter with highaccuracy. It extracts printing dots that appears for the first time whenscanning a printed image while searching for printing dots in a specificdirection, measures the inclination of a straight line, approximated bythe extracted dot string as the inclination of an input image andcorrecting the read printed image by linearly transforming the measuredinclination as a rotation parameter.

SUMMARY OF THE INVENTION

A poor recording detection device in the major aspect of the presentinvention forms dots on a recording medium on the basis of inputrecording data and detects poor recording when recording it. The poorrecording detection device comprises an illumination unit for applyingillumination light to the recording medium after the recording isperformed and a camera unit for shooting and sensing the image recordedon the recording medium to which the illumination unit applies theillumination light and outputting detected information. After specifyinga reference recording data as input recording data and recording it areference recording image on the recording medium, the poor recordingdetection device outputs reference detected information by which thecamera unit checks the reference recording image, generates correctioninformation by comparing the reference detected information with thereference recording data and makes corrected input recording datacorrected on the basis of the correction information of the inputrecording data. The poor recording detection device further comprises apoor recording determination unit for determining whether there is thepoor recording on the basis of the comparison result between the inputrecording image information detected and obtained by the camera unitwith the correction input recorded data after recording the inputrecording data on the recording medium as an input recording image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the conceptual block configuration at the time of thecalibrating operation of the poor recording detection device in thefirst preferred embodiment.

FIG. 2 shows the arrangement of each component of the poor recordingdetection device.

FIG. 3 shows the conceptual block configuration at the time of thenormal recording operation of the poor recording detection device in thefirst preferred embodiment.

FIG. 4A shows one example of reference recording data being thereference for calibration.

FIG. 4B bi-dimensionally shows data detected as reference detectedinformation by the camera unit after recording reference recording dataon a recording medium.

FIG. 4C shows one example of correction information.

FIG. 4D shows one example of a correction information string.

FIG. 4E shows one example of input recording data.

FIG. 4F shows one example of a correction information string.

FIG. 4G shows one example of corrected input recording data.

FIG. 4H shows one example of input recording image information.

FIG. 4I shows a poor determination result obtained when performing thiscorrection process.

FIG. 4J shows a poor determination result obtained when not performingthis correction process.

FIG. 5 shows a gradation correction characteristic by gradationcorrection information.

FIG. 6A shows an example of the image pattern of reference recordingdata.

FIG. 6B shows an enlarged image pattern gradation information portion ofthe reference recording data.

FIG. 7 shows the conceptual block configuration at the time of thecalibrating operation of the poor recording detection device in avariation of the first preferred embodiment.

FIG. 8A shows one example of the reference recording data being thereference for calibration.

FIG. 8B bi-dimensionally shows data detected as reference detectedinformation by the camera unit after recording reference recording dataon a recording medium.

FIG. 8C shows one example of correction information.

FIG. 8D shows one example of a correction information string.

FIG. 8E shows one example of input recording data.

FIG. 8F shows one example of a correction information string.

FIG. 8G shows one example of corrected input recording data.

FIG. 8H shows one example of input recording image information.

FIG. 8I shows one example of a nozzle missing determination threshold.

FIG. 8J shows a poor determination result obtained when performing thiscorrection process.

FIG. 8K shows a poor determination result obtained when not performingthis correction process.

FIG. 9 shows the conceptual block configuration at the time of thecalibrating operation of the poor recording detection device in thesecond preferred embodiment.

FIG. 10A shows one example of the reference recording data being thereference for calibration.

FIG. 10B bi-dimensionally shows data detected as reference detectedinformation by the camera unit after recording reference recording dataon a recording medium.

FIG. 10C shows one example of correction information.

FIG. 10D shows one example of a correction information string.

FIG. 10E shows one example of input recording data.

FIG. 10F shows one example of a correction information string.

FIG. 10G shows one example of corrected input recording data.

FIG. 10H shows one example of input recording image information.

FIG. 10I shows one example of a nozzle missing determination threshold.

FIG. 10J shows a poor determination result obtained when performing thiscorrection process.

FIG. 10K shows a poor determination result obtained when not performingthis correction process.

FIG. 11 shows the conceptual block configuration at the time of thenormal recording operation of the poor recording detection device in thesecond preferred embodiment.

FIG. 12 shows the conceptual block configuration of the image correctionunit in the poor recording detection device in the third preferredembodiment.

FIG. 13 shows the method for extracting reference recording data frominput recording data, of the image correction unit in the poor recordingdetection device in the third preferred embodiment.

FIG. 14 is a flowchart for extracting reference recording data frominput recording data, of the image correction unit in the poor recordingdetection device in the third preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments of the present invention with reference to thedrawings below. In the following description, the carrying direction ofa recording medium and the direction diagonal to this carrying directionare defined as a sub-scanning direction and a main scanning direction,respectively.

FIG. 1 shows the conceptual block configuration at the time of thecalibrating operation of the poor recording detection device in thefirst preferred embodiment. FIG. 2 shows the arrangement of eachcomponent of the poor recording detection device in the image recordingapparatus 30 in this preferred embodiment.

Input recording data 2 is inputted to the image recording apparatus 30from a higher-level device, such as a personal computer (PC) or thelike. The image recording apparatus 30 records an image on a recordingmedium 3, such as paper, film or the like, on the basis of this inputrecording data 2. The poor recording detection device 1 in thispreferred embodiment detects poor recording, for example, by dischargingink from the nozzle of an ink-jet recording head and fusing it whenrecording an image composed of linearly or bi-dimensionally arrayeddots.

The poor recording detection device 1 comprises a camera unit 4, anillumination unit 5, a carrier unit 6, a recording unit 7 and a controlunit 8. The control unit 8 comprises at least reference recording datamemory 9, an image correction unit 10 including an operation unit 10 aand correction information memory 10 b and a poor recordingdetermination unit 11.

The input recording data 2 being basic recording information transmittedfrom a higher-level device is inputted to the control unit 8. Thecontrol unit 8 has normal control functions as the image recordingapparatus 30, to develop image data and enable the recording head of therecording unit 7 to discharge ink with appropriate mapping and density,to operate the carrier unit 6, to adjust recording timing with therecording head and the like. The image recording apparatus 30 comprisesthe paper feeding unit, paper ejecting unit and the like, which are notshown in FIG. 1, of the recording medium 3.

The camera unit 4 shoots the image of the recording medium 3 recorded asdescribed above and converts the obtained image (detected information)into digital data. The illumination unit 5 applies light to the recordedrecording medium 3 to form a secondary light source surface forshooting. Furthermore, the carrier unit 6 moves the recorded recordingmedium 3 to within the effective view range of the camera unit 4 and theillumination unit 5.

The control unit 8 controls recording medium shooting timing with thecamera unit 4, the illumination unit 5, the carrier unit 6 and therecording unit 7 and unifies the acquisition of the input recording data2 transmitted from a higher-level device, the control of the recordingunit 7, a pre-treatment for comparing with image information detected bythe camera unit 4, the acquisition of the image information detected bythe camera unit 4 and the like.

The control unit 8 also controls the image correction unit 10 and thepoor recording determination unit 11 for determining whether there ispoor recording when recording on the recording medium 3.

The control unit 8 comprises a circuit composed of a micro processorunit (MPU) having a control function and an operation function, and astorage unit, such as, ROM, etc., storing a control program and thelike, and non-volatile memory, which is not shown in FIG. 1, storingsetting values for controlling devices and the like. The control unit 8also realizes the above-described various controls by the MPU reading aprescribed control program from the storage unit and executing it.

When obtaining the input recording data 2 transmitted from ahigher-level device in recording, the control unit 8 temporarily storesthe data in its memory, which is not shown in FIG. 1. Then, it transfersthe image data in the first line˜the n-th line (n=integer of 2 or more)to the recording unit 7 and records it.

Next, each component of the poor recording detection device 1 isdescribed with reference to FIG. 2.

The carrier unit 6 is disposed in such a way that the recording medium 3moves in the sub-scanning direction by rotating a pair of carrierrollers 6 a, and carries the recording medium 3 while maintaining theopposed relationship between the surface of the recording medium 3 andthe camera unit 4. Then, the carrier unit 6 moves the recorded recordingmedium 3 to within the effective view range of the camera unit 4 and theillumination unit 5.

The four color recording heads 7-1 (black), 7-2 (cyan), 7-3 (magenta)and 7-4 (yellow) of the recording unit 7 are disposed on the upperstream side of the camera unit 4.

By such an arrangement, the recording state of the recording medium 3,immediately after the recording can be detected in real time. Thecontrol unit 8 can be disposed in an arbitrary position.

The irradiation range of the illumination unit 5 is arranged in such away that the light receiving area of line sensor 4 a in the camera unit4 can cover the view of applied recording medium 3 and linearly applieslight to the recording medium 3. The illumination unit 5 comprises alight source for linearly emitting light as a light source forilluminating a long range in which the amount of light is distributedlinearly uniformly. For such a light source, although, for example, afluorescent lamp can be used, light emitting diodes (LED) linearlyarranged can be also used. When an LED is used, the device can beminiaturized.

Although a light source, such as infrared/ultraviolet rays, sun rays orthe like can be also used according to the ink of the recording head,the reflective characteristic of the recording medium 3 and the like, inthat case it is preferable to match the wavelength sensitivitycharacteristic of the line sensor of the camera unit 4 with thewavelength of the light source from the viewpoint of detectionsensitivity. When it is necessary to shoot in a high speed in order toimprove the carrying speed of the recording medium 3, a larger amount oflight is necessary. In this case, the illumination unit 5 can alsoadopt, for example, a configuration in which a metal halide lamp is usedas a light source, illumination light is led to the illumination unit 5using an optical fiber and this illumination light is linearly appliedto the recording medium 3.

A line sensor 4 a using a charge-coupled device (CCD) and acomplementary metal oxide semiconductor (CMOS) and a lens 4 b are builtin the camera unit 3. In this case, the pixel array of the line sensor 4a is disposed in such a way that the direction in which the array isprojected on the surface of the recording medium 3 can be the mainscanning direction. Therefore, the line sensor 4 a can continuously reada bi-dimensional image recorded on the recording medium 3 carried by thecarrier unit 6.

Instead of the line sensor 4 a in the camera unit 4, bi-dimensionallyarrayed area sensors can be also used. In that case, by using anillumination system of bi-dimensionally lighting the view field of thelight receiving surface of the area sensor which is projected on thesurface of the recording medium 3, the output of an encoder devicedisposed in the carrier unit 6 or the like, image information isintermittently obtained in a appropriate shooting timing according tothe carrier speed. By setting each distance between the recording medium3, the lens 4 b and the line sensor 4 a, a desired resolution accordingto the pitch of a pixel array and an optical scale factor can beobtained.

The camera unit 4 is disposed in such a way that the direction of theoptical axis may be perpendicular to the surface of the recording medium3 and the irradiation axis 5 b of the illumination unit 5 (see FIG. 2)is disposed in such a way as to be, for example, 45 degrees against thesurface of the recording medium 3 in a plane formed by the sub-scanningdirection and a direction perpendicular to the surface of the recordingmedium 3. Since by such an arrangement, the regular reflection light ofillumination light reflected on the surface of the recording medium 3can be prevented from entering the camera unit 4, the camera unit 4 canshoot and pick up a good-contrast image.

The control unit 8 and the poor recording determination unit 11 aredisposed physically away from the recoding unit 7, the carrier unit 6,the camera unit 4 and the illumination unit 5. The control unit 8obtains the input recording data 2 transmitted from a higher-leveldevice and compares it with image information outputted from the cameraunit 4.

The poor recording detection device 1 continuously reads an imagerecorded on the recording medium 3 by the line sensor 4 a on the basisof the input recording data 2 transmitted from a higher-level device andcompares the obtained information with the input recording data 2transmitted from a higher-level device. Then, on the basis of thiscomparison result, the poor recording detection device 1 detects poorrecording in which ink is not appropriately discharged due to inkclogging, the poor operation of a nozzle or the like and poor fusion inwhich ink does not reach the target position on the recording medium 3.

Next, the correction method in poor recording detection by the poorrecording detection device 1 is described with reference to FIGS. 1 and3.

In the following description, image data transmitted from a higher-leveldevice is indicated by the input recording data 2 as described above andinput recording data being a fixed image recording pattern used at thetime of calibration for correction is indicated by reference recordingdata, which are registered in advance in the above-described referencerecording data memory 9.

The reference recording data recorded on the recording medium 3 isindicated by a reference recording image 3 a, image data obtained byreading this recorded reference recording image 3 a by the camera unit 4is specified as reference detection information and a correction valueobtained by comparing the reference recording data with the referencedetection information is indicated by correction information.Furthermore, image data obtained by correcting the input recording data2 by the correction information is indicated by corrected inputrecording data, an image recorded on the recording medium 3 on the basisof the input recording data 2 is indicated by an input recording image 3b and image data obtained by reading this input recording image 3 b bythe camera unit 4 is specified as input recording image information.Then, by comparing the corrected input recording data with the inputrecording image information by the poor recording detection unit 11,poor recording is detected.

This data has 24-bit data being the total of 8-bit data for each colorof RGB. In this case, in the dot data of each color of RGB expressed by8 bits, the lowest and highest gradation values are 0 and 255,respectively. In the recording medium 3 appropriately recorded on thebasis of the input recording data, the gradation of recording dotcorresponding to dot data whose gradation value is the lowest (that is,0) is expressed to be black. In the recording medium 3 appropriatelyrecorded on the basis of the input recording data 2, the gradation ofrecording dot corresponding to dot data whose gradation value is thehighest (that is, 255) is expressed to be white.

However, when being appropriately recorded on the basis of the inputrecording data 2, the recording dot corresponding to dot data whosegradation value is the highest becomes a non-recording dot (dot in whichink drop to be fused into the recording medium 3 is not discharged).“Poor recording” includes not only a poor recorded image due to the dotmissing of an image recorded on the recording medium 3 and poorgradation and the like but also a poor recording medium 3, such as poorpreprint printed in advance on the recording medium 3, a broken or dirtyrecoding medium and the like.

The poor recording detection device 1 in this preferred embodiment isconfigured to detect poor recording in which ink is not appropriatelydischarged due to ink clogging, the poor operation of a nozzle and thelike, poor fusion in which ink does not reach the target position on therecording medium 3 and partially poor recording medium 3 by continuouslyreading an image recorded on the recording medium 3 on the basis of theinput recording data 2 by the line sensor 4 a and comparing the obtainedimage information the input recording data 2 transmitted from ahigher-level device.

Therefore, in order to accurately detect poor recording the highmatching of the intra-plane positions and gradation values ofcorresponding dot data are necessary. However, actually there are thefollowing various problems. For example, sometimes intervals betweennozzle positions corresponding to each dot of the recording unit 7 arepartially unequal and sometimes an image forming position on the linesensor 4 a deviates and is fixed in the main scanning direction due tothe aberration of a camera lens 4 b. Sometimes density after recordingdoes not becomes uniform in the main scanning direction due to theunevenness of the proper characteristic of a recording head, such as theunevenness of the amount of discharge, discharge condition of ink of thenozzle of each of the recording heads 7-1, 7-2, 7-3 and 7-4 andsometimes the reflectance of the recording medium 3 differs for eachtype of medium. Furthermore, sometimes the unevenness of illuminationlight and the decrease of the peripheral amount of light of the cameralens 4 b occur and are fixed. Sometimes the position of the recordingunit 7 deviates against the recording medium 3 and an image deviates andis recorded. Sometimes the recording medium 3 moves obliquely againstthe recording unit 7, and an image deviates obliquely and is recorded.

When the positions and gradation values of compared dot data is notmatched due to these factors, the poor recording detection functiondeteriorates.

In order to remove these position and gradation errors, in thispreferred embodiment, firstly, as shown in FIG. 1, the referencerecording data having a pre-determined bi-dimensional array pattern andgradation information in the operation mode of calibration forcorrection, different from the normal printing operation is registeredin the reference recording data memory in advance and the control unit 8connects the reference recording data to the image correction unit 10and recording unit 7 by a switch (SW01).

By such an operation, the reference recoding image 3 a recorded on therecording medium 3 by the recording unit 7 is moved up to within theview field of the camera unit 4 by the carrier unit 6 and is detected asthe reference detection information by the camera unit 4. At this time,the reference recording image 3 a is picked up as reference detectioninformation including the peculiar characteristic of the recording heads7-1, 7-2, 7-3 and 7-4 of the image recording apparatus 30 and the errorsof the peculiar position and gradation of the poor recording detectiondevice 1 and is led to the image correction unit 10 by a switch (SW02).

By the above-described process, the reference recording data and thereference detection information gather in the image correction unit 10and they are compared and operated by the operation unit 10 a. Theobtained difference between them is the correction information forposition and gradation and is stored in the correction informationmemory 10 b of the image correction unit 10.

Then, the normal recording operation shown in FIG. 3 is performed. Thisrecorded data selects the input recording data 2 by the change-over ofthe switch (SW01) and supplies it to the recording unit 7 and the imagecorrection unit 10. The input recording image 3 b recorded on therecording medium 3 by the recording unit 7 is moved up to within theview field of the camera unit 4 by the carrier unit 6 and is detected bythe camera unit 4. At this time, the input recording image 3 b is pickedup as input recording image information including the errors of thepeculiar position and gradation of the poor recording detection device 1and is connected to the poor recording determination unit 11 by thechange-over of the switch (SW02).

The other input recording data 2 connected to the image correction unit10 by the switch (SW01) calls up the correction information obtained inadvance when calibrating from the correction information memory 10 b inthe image correction unit 10 and adds the correction information to theinput recording data 2.

By this process, the input recording data 2 becomes corrected inputrecording data being data including the errors of the peculiar positionand gradation of the poor recording detection device 11 and becomesreference data used for the comparison process in the poor recordingdetermination unit 11.

By the above-described process, data necessary for determination gathersin the input unit of the poor recording detection device 11 and the poorrecording caused when recording the input recording data 2 can bedetected by obtaining the difference between the corrected inputrecording data and the input recording image information in the poorrecording detection device 11.

Since the above-described configuration presumes handling the inputrecording data by the RGB 24 bits, the other units also presume aconfiguration corresponding to color. For example, the recording unit 7performs color conversion in order to record RGB color information by ahead corresponding to CMYK ink, the camera unit 4 detects the inputrecording image 3 b in RGB by detecting the received amount of lightafter transmitting the input recording data 2 through each color filterof RGB by the line sensor 4 a and further all the units included in thecontrol unit 8 perform processes corresponding to the 3 channels of RGB.For example, the image correction unit 10 performs dot positioncorrection, gradation correction and the like.

The poor recording determination unit 11 can specify the poor dot ofeach recording head of CMYK by converting RGB into CMYK again. Ifmonochrome recording is presumed, it is sufficient for theabove-described units to take a one-channel configuration. Therefore,the system can be simplified.

Here, the procedure of obtaining correction information on the basis ofthe reference recording data in the calibrating operation of theconfiguration shown in FIG. 1 and adding position correction informationto the input recording data to generate corrected input recording datain the normal recording operation of the configuration shown in FIG. 3is described with reference to FIG. 4. In FIG. 4, the main and subscanning directions are intra-paper surface rightward and downwarddirections, respectively.

Firstly, in FIG. 4A, one dot corresponds to one black circle, forexample, in the recording density of 300 dpi assuming the referencerecording data being the reference for calibration to be a four-rowfour-column bi-dimensional image matrix. In this case, the recordingdensity of the nozzle array of the recording head is also 300 dpi. Theposition of a black circle indicates the position of a dot to berecorded and corresponds to each nozzle position of the recording head,linearly arrayed in the main scanning direction. Although each dot alsoincludes color and gradation information, only position information isshown in FIG. 4 for the purpose of simplification.

Each nozzle of the recording head is on/off-controlled in time sequenceto record the reference recording data on the recording medium whichmoves in the sub scanning direction on the basis of its dots in the subscanning direction.

FIG. 4B bi-dimensionally shows data detected as reference detectioninformation by the camera unit 4 after the reference recording data isrecorded on the recording medium 3. The space resolution of the cameraunit 4 is, for example, 600 dpi being the double of the above-describedrecording density of 300 dpi. A dot (3, 2) on the third row in the subscanning direction and on the second column in the main scanningdirection shown in FIG. 4A is detected as a dot (5, 2) in FIG. 4B.Similarly, dots (4, 2), (1, 3) and (2, 3) shown in FIG. 4A are detectedas (7, 2), (1, 6) and (3, 6), respectively, in FIG. 4B.

This is, for example, because the reference recording data deviates byhalf of one dot pitch, that is, one pixel pitch of the line sensor 4 adeviates if the line sensor 4 a has resolution of 600 dpi due to thepositional deviation initially owned by the recording head. FIG. C showscorrection information obtained by mapping the direction and size ofthis deviation in the main scanning direction in relation to the arrayof the reference recording data, for example, assuming the left side,the right side and one dot pitch corresponding to 600 dpi as minus (−),plus (+) and 1, respectively, by comparing and operating the referencerecording data and reference detection information. A dot which does notdeviate is indicated by 0.

FIG. 4D shows the correction information string of the positiondeviation information compressed in the sub scanning direction since ithas one value for each nozzle. This correction information string isstored in the correction information memory 10 b of the image correctionunit 10 shown in FIG. 1.

Next, the process of generating the corrected input recording data byadding the correction information to the input recording data 2 in thenormal recording operation in the configuration shown in FIG. 3 isdescribed. In normal recording operation, the position information ofthe input recording data shown in FIG. 4E is mapped in advance with 600dpi being the same space resolution as the camera unit 4 and thecorrection information and the corrected input recording data shown inFIG. 4G can be obtained by adding the correction information stringshown in FIG. 4D stored in the correction information memory 10 b of theimage correction unit 10 shown in FIG. 1, as shown in FIG. 4F.

By this process, the input recording data 2 becomes corrected inputrecording data being data including the peculiar position error of thepoor recording detection device 1 and becomes reference data used in thecomparison of the poor recording determination unit 11.

Then, as described above, by calculating the difference between thecorrected input recording data and the input recording information inthe poor recording determination unit 11, poor recording caused whenrecording the input recording data can be detected.

By the above-described configuration, for example, as shown in a stringto be corrected shown in FIG. 4H, when a nozzle in the second column ofthe main scanning direction does not discharge to cause dot missing, bycomparing the corrected input recording data shown in FIG. 4G with theinput recording image information shown in FIG. 4H in the poor recordingdetermination unit 11, the poor recording of each dot is checked in theorder of T, F, T and T along the main scanning direction as shown inFIG. 4I poor recording check (to be corrected) and it is correctlydetermined that only the nozzle in the second column of the mainscanning direction. In this case, T and F indicate a dot with no poorrecording and a dot with poor recording. In FIGS. 4G and 4H, thepositions in the main scanning direction of a nozzle string for fourcolumns in this example are related by resolution for eight columns.

However, when the poor recording is detected without adding correctioninformation to the input recording data 2, the poor recording of eachdot is checked in the order of T, F, F and T along the main scanningdirection as shown in FIG. 4J poor recording check (no need to correct)since the input recording data in shown in FIG. 4E is compared with theinput recording image information shown in FIG. H, and essential dotmissing cannot be detected. Furthermore, a dot without dot missing inthe third column is wrongly detected.

Next, the procedure of calculating correction information on the basisof the reference recording data in the calibrating operation of theconfiguration shown in FIG. 1 and generating corrected input recordingdata by adding gradation correction information to the input recordingdata 2 in the normal recording operation is described with reference toFIG. 5.

FIG. 5 is a graph showing the co-relationship between the gradationinformation of reference recording data and the gradation value ofreference detection information detected by the camera unit 4 afterrecording the reference recording data on the recording medium takingthe former and the latter for the X and Y axes, respectively. Thegradation value of the reference recording data does not always coincidewith the gradation value of the reference recording image informationdue to the characteristics of the recording heads 7-1, 7-2, 7-3 and 7-4,the peculiar characteristic of the poor recording detection device 1,the characteristic of used ink, the characteristics of the color,reflectance and the like of the recording medium 3, and has, forexample, co-relation characteristic expressed by Y=f(X).

In this example, for example, the recording medium 3 is not completelywhite and light color is attached to white. A characteristic thatproportional dark gradation cannot be obtained due to blur as recordingwith high density is shown. As to a nozzle, one characteristic shown inFIG. 5 is given to each dot of the linear array corresponding to eachnozzle string of the recording head in advance. A correction informationstring is a data string with the same resolution of 600 dpi as in FIG.4D. By adding this correction information string to the input recordingdata and applying the operation of Y=f(X) to the input recording data asin the above-described position deviation correction, corrected inputrecording data being data corrected by the peculiar gradation error ofthe poor recording detection unit 1 and the like and by calculating adifference in gradation between the corrected input recording data andthe input recording image information in the poor recordingdetermination unit 11, poor recording caused when recording the inputrecording data can be detected.

Furthermore, only gradation correction can be performed withoutperforming the above-described nozzle position correction. In this case,it is sufficient to make only a value for gradation correction of thecorrection information calculated in the image correction unit 10 bycomparing the reference recording data with the reference detectioninformation in the calibrating operation valid and to compulsorily input0 to a memory unit for nozzle position, that is, not to perform nozzleposition correction.

Thus, by selectively using the position and gradation portions of thecorrection information, not only poor recording due to thedischarge/non-discharge of each nozzle can be accurately detected, butalso a poorly recorded image can be detected and image quality can beevaluated comprehensively.

Next, FIG. 6A shows an example of the image pattern of the referencerecording data shown in FIG. 1. This image pattern is provided for eachcolor (four colors in this preferred embodiment). The image range 20 ofthe reference recording data are provided with a recording area 21composed of an area from patterns 21-1 to 21-8 in eight steps obtainedby dividing 0 to 255 gradation and a portion 21-9 corresponding to eachnozzle of the recording head.

By detecting the gradation values of the area from 21-1 until 21-8 usingthe camera unit 4 and relating them to the gradation values of thereference recording data, the gradation correction characteristic shownin FIG. 5 can be easily obtained. The length 22 in the main scanningdirection of the recording area 21 is made longer than the length in themain scanning direction of the recording head,

FIG. 6B shows the enlarged drawing of the portion 21-9 shown in FIG. 6A.In FIG. 6B, the intra-paper rightward and downward sides are the mainand sub scanning directions, respectively. For example, one pixel 24corresponding to one dot of the reference recording data corresponds tothe nozzle column No. 15 of the recording head and this nozzle columnrecords the 23-th to the 27-th dots in the sub scanning direction.

Numerical reference 25 indicates the print area of the nozzle string 1from the third dot until the seventh dot in the sub scanning direction.In this dot pattern, for example, a section of the third˜seventh dots inthe sub scanning direction is printed every five columns that is, innozzle columns 1, 6, 11 . . . and their adjacent nozzles do not printsimultaneously.

By arraying recorded data dots thus, interference between adjacentnozzles due to blur and the resolution shortage of the camera system,caused when recording in the comparison/operation process afterdetection can be reduced and a position error can be easily detected inthe comparison/operation with the reference recording data in the imagecorrection unit 10 after detecting the reference recording data asreference detection information in the camera unit 4 after recoding thereference recording data on the recording medium 3.

FIG. 7 shows a variation of the above-described first preferredembodiment, which is configured to use the input recording data 2transmitted from a higher-level as the reference recording data whencalibrating. For this recording data, the pattern shown in FIG. 6 can beused. Alternatively, another pattern can be used as long as a dotposition in the main scanning direction and a gradation characteristiccan be obtained and there is no problem if it is provided in the inputrecording data instead of inside the poor recording

The input recording data used when normally recording can be also usedas the reference recording data. For the configuration at the time ofthe normal recording operation in this variation, the same configurationshown in FIG. 1 as described above can be used. For the correctioninformation, both or one of the above-described position correctioninformation and the gradation correction information can be used.

As described above, according to the first preferred embodiment, sincethere is no need to correct for each page, a poor recording detectiondevice capable of printing in a high speed and accurately detectingwithout being affected by the printing position deviation and gradationerror initially owned by a printer can be provided.

The pixel pitch of the line sensor 4 a for reading a recorded image canbe the double of the dot pitch of the recorded image and the dotposition can be accurately detected. Therefore, the degree of matchingof the intra-plane position and gradation of corresponding dot data canbe improved to accurately detect poor recording.

Furthermore, the pixel pitch of the line sensor 4 a is not limited tothe double of the dot pitch of an image to be recorded and it can bemore than it or equal to it. In the case position correction for eachdot or gradation correction is not needed, the pixel pitch of the linesensor 4 a can also be less than the dot pitch of the recorded image.

In the case the reference detection information of all the dots is notnecessary, there is no need for the line sensor 4 a to be equal to orwider than the recording width recorded on the recording medium 3 and itis sufficient if its necessary portion is be equal to or wider than therecorded recording width. In this case, for example, a calibrationpattern can be provided only in the four corners of the recording rangeof the recording medium 3, only these portions can be read and the colorof the recording medium 3, position deviation between the recording unit7 and the recording medium 3 and the like can be detected and corrected.

Next, the second preferred embodiment of the poor recording detectiondevice of the present invention is described. In the description of thesecond preferred embodiment, the same numerical references are attachedto the same components as the above-described first preferred embodimentand their description of the same functions and effects as the firstpreferred embodiment are omitted.

As to the second preferred embodiment, the procedure of obtainingcorrection information after weighting the reference detectioninformation detected from the reference recording data by highresolution, according to its density value in the calibrating operationshown in FIG. 1 of the above-described first preferred embodiment andgenerating corrected input recording data by adding position correctioninformation to the input recording data in the normal recordingoperation of the above-described configuration shown in FIG. 3 isdescribed with reference to FIG. 8. In FIG. 8, the main and sub scanningdirections are intra-paper surface rightward and downward directions,respectively. In FIG. 8, numerical numbers attached to each pixelindicate density values, and white and black are indicated by 0 and 255,respectively.

Firstly, in FIG. 8A, as in FIG. 4A, one dot corresponds to one blackcircle, for example, in the recording density of 300 dpi assuming thereference recording data being the reference for calibration to be afour-row four-column bi-dimensional image matrix. In this case, therecording density of the nozzle array of the recording head is also 300dpi. The position of a black circle indicates the position of a dot tobe recorded and corresponds to each nozzle position of the recordinghead, linearly arrayed in the main scanning direction. Although each dotalso includes color and gradation information, only position informationis shown in FIG. 8 for the purpose of simplification.

Each nozzle of the recording head is on/off-controlled in time sequenceto record the reference recording data on the recording medium whichmoves in the sub scanning direction on the basis of its dots in the subscanning direction.

FIG. 8B bi-dimensionally shows data detected as reference detectioninformation by the camera unit 4 after the reference recording data isrecorded on the recording medium 3. The space resolution of the cameraunit 4 is, for example, 600 dpi being the double of the above-describedrecording density of 300 dpi. For example, a dot (3, 4) in the third rowof the sub scanning direction and in the fourth column of the mainscanning direction shown in FIG. 8A is detected as a dot between pixels(5, 7) and (5, 8) in FIG. 8B and the density value ratio between thepixels are 0.7 to 0.3.

This shows a state where the reference recording data deviates by adistance shorter than one dot pitch, for example, due to the dischargedeviation of each nozzle initially owned by the recording head. Then, bycomparing the reference recording data with the reference detectioninformation and operating its difference in the above-described imagecorrection unit 10, the directions and sizes of this deviation in themain and sub scanning directions are obtained. For example, thecorrection information shown in FIG. 8C shows values obtained bynormalizing a density value corresponding to each dot in the range ofadjacent pixels. A dot with no deviation is indicated by 1.

FIG. 8D shows a correction information string obtained by compressingposition deviation information in the sub scanning direction since thenumber of values of the position deviation information is one for eachnozzle. This correction information string is stored in the correctioninformation memory 10 b of the above-described image correction unit 10shown in FIG. 1. In this example, each string takes the average ofdensity values after normalizing in the sub scanning direction. If thedispersion of the density values in the sub scanning direction is largeand periodic, the correction information can be also treatedbi-dimensionally instead of linearly as described later.

Next, the process of generating corrected input recording data by addingcorrection information to the input recording data 2 when normallyrecording in the configuration shown in FIG. 3 is described. Whennormally recording, by mapping the position information of the inputrecording data shown in FIG. 8E in advance with 600 dpi being the samespace resolution as the camera unit 4 and the correction information andmultiplying the correction information string shown in FIG. 8D which isstored in the correction information memory 10 b of the image correctionunit 10 shown in FIG. 1, as shown in FIG. 8F, the corrected inputrecording data shown in FIG. 8G can be obtained. For example, the valueof a pixel (7, 7) shown in FIG. 8G becomes 131, which is obtained bymultiplying 187 being the value of the pixel (7, 7) shown in FIG. 8E by0.7 of the correction information string shown in FIG. 8D.

By this process, the input recording data 2 becomes corrected inputrecording data being data including the peculiar position error of thepoor recording detection device 1 and becomes reference data used forcomparison in the poor recording determination unit 11.

Then, in the poor recording determination unit 11, the nozzle missingcheck threshold shown in FIG. 8H is generated. Although in this example,a value obtained by multiplying each pixel value of the corrected inputrecording data shown in FIG. 8G by 0.5 is the check threshold, thisvalue can be arbitrarily set taking into consideration a detection ratioand a printing system. Then, by comparing the size relationship betweenthe nozzle missing check threshold and the input recording imageinformation, poor recording caused when recording the input recordingdata can be detected. In this example, it is determined that the nozzlein the second column is missing.

By the above-described configuration, for example, when dot missingoccurs due to the missing of the nozzle in the second column of the mainscanning direction, as shown in a string to be corrected of FIG. 8H, bycomparing the nozzle missing check threshold shown in FIG. 8H with theinput recording image information shown in FIG. 8I in the poor recordingdetermination unit 11, the poor recording of each dot is checked in theorder T, F, T and T along the main scanning direction as shown in poorrecording check of FIG. 8J and it is correctly determined that only thenozzle in the second column of the main scanning direction is missing. Tand F indicate dots with poor recording and without poor recording,respectively. In FIGS. 8H and 8I, the position in the main scanningdirection of nozzle strings for four columns in this example are relatedwith resolution for eight columns.

However, when detecting poor recording without adding correctioninformation to the input recording data 2, since the input recordingdata shown in FIG. 8E is compared with the input recording imageinformation shown in FIG. 8I, the poor recording of each dot is checkedin the order of T, F, F and T along the main scanning direction, asshown in poor recording determination (not to be corrected) of FIG. 8Kand it is wrongly determined the dots in the third and fourth columnswithout nozzle missing were missing.

Instead of operating a density value in order to obtain FIG. 8G, theaverage of those of adjacent pixels when obtaining the correctioninformation shown in FIG. 8C can be also calculated, a pixel with thehighest density can be also selected or a correction value can be alsocalculated by calculating gravity on the basis of the position anddensity value of each pixel. Thus, by obtaining reference detectioninformation with higher density than the dot density of the recordinghead and checking nozzle missing using correction information obtainedaccording to the brightness information of each pixel, more accuratenozzle missing check than a nozzle pitch can be realized.

In order to more accurately detect dot position deviation due to themis-direction of the recording head, the discharge timing fixed error ofthe head, the control error of a carrier system, the uneven fixedcarrier speed against page starting timing, the mechanical eccentricityand shape error of a carrier system, which are peculiar to the imagerecording apparatus, it is sufficient to multiply FIG. 8C being thecorrection information of a bi-dimensional array whose area is formed inarbitrary units to each pixel corresponding to the input recording datainstead of multiplying it by a linear correction information string whenmultiplying in FIG. 8F. If the load of a processing system and a memoryaccess system is increased by using bi-dimensional correctioninformation, it is sufficient to switch over to linear correctionarbitrarily.

Next, a variation of the above-described second preferred embodiment isdescribed with reference to FIGS. 9 and 10. FIG. 9 shows the conceptualblock configuration of the poor recording detection device in avariation of the second preferred embodiment of the present inventionand shows its calibrating operation. FIG. 10 shows its normal recordingoperation. FIG. 9 differs from FIG. 1 in that SW03 is provided as theroute change-over switch of the input recording data 2 instead of SW01and that SW02 is always connected to the block of the operation unit 10a and the correction information memory 10 b.

As to its operation, firstly, when calibrating, SW03 switches over tothe state indicated by a broken line to make the flow of a signal thesame as in FIG. 1. At this time, the correction information is stored inthe correction information memory 10 b as in the first preferredembodiment.

Then, when normally recording, SW03 switches over to the state indicatedby a solid line to transmit the input recording data to the recordingunit 7 and also transmits it to the poor recording determination unit 11directly without passing it through the operation unit 10 a. In the poorrecording determination unit 11, the other information to be compared isread by the camera unit 4 after the input recording data 2 is recordedon the recording medium 3 and is transmitted to the operation unit 10 aas input recording image information via SW02. Then, after operating iton the basis of the correction information stored in the correctioninformation memory 10 b when calibrating, it is transmitted to the poorrecording determination unit 11 as corrected input recording imageinformation, and is compared with the above-described input recordingdata 2 and is checked. Although in the second preferred embodiment, thecorrection information is added to the input recording data 2 and isoperated, in this variation, the correction information is added to theinput recording image information and is operated.

Then, the procedure of obtaining correction information on the basis ofthe reference recording data when calibrating in the configuration shownin FIG. 8 and generating corrected input recording image information byadding position correction information to the input recording imageinformation when normally recording in the configuration shown in FIG. 9is described with reference to FIG. 10.

FIG. 10 differs from FIG. 8 in that FIG. 10E is input recording imageinformation instead of input recording data and that the operation inFIG. 10F is division instead of multiplication. The difference incomparison/determination between the cases with correction and withoutcorrection and their effects are the same as in FIG. 8.

By adding correction information to the input recording imageinformation and operating them thus, the processing system can besometimes simplified. For example, this is a case where the resolutionof the input recording data 2 and that of the camera unit 4 are 300 dpiand 600 dpi, respectively. In such a case, since if the 300 dpi of theinput recording data 2 is made 600 dpi, the amount of information tendsto increase, the load of the processing system increases. Therefore, itis easier to generate 300 dpi reference recording data from 600 dpicamera image data. In this case, it is sufficient to performoptimization, such as making a density value weighted on the basis ofthe gravity position from each 600 dpi adjacent center pixel the densityvalue of corresponding 300 dpi pixel, taking the average of those of 600dpi pixels, selecting that of one of the pixels or the like according toits detection accuracy.

As described above, according to the above-described second preferredembodiment, since there is no need to correct for each page, a poorrecording detection device capable of printing in a high speed andaccurately detecting without being affected by the printing positiondeviation and gradation error initially owned by a printer can beprovided.

By making the pixel pitch of the line sensor 4 a for reading recordedimaged the double of the dot pitch of an image to be recorded, a dotposition can be more accurately detected. Therefore, the degree ofcoincidence of the intra-plane position and gradation values ofcorresponding dot data can be improved and poor recording can be moreaccurately detected.

Furthermore, the pixel pitch of the line sensor 4 a is not limited tothe double of the dot pitch of an image to be recorded and it can bemore than it or equal to it. In the case position correction for eachdot or gradation correction is not needed, the pixel pitch of the linesensor 4 a can also be less than the dot pitch of the recorded image.

In the case the reference detection information of all the dots is notnecessary, there is no need for the line sensor 4 a to be equal to orwider than the recording width recorded on the recording medium 3 and itis sufficient if its necessary portion is be equal to or wider than therecorded recording width. In this case, for example, a calibrationpattern can be provided only in the four corners of the recording rangeof the recording medium 3, only these portions can be read and the colorof the recording medium 3, position deviation between the recording unit7 and the recording medium 3 and the like can be detected and corrected.

Next, the third preferred embodiment of the poor recording detectiondevice of the present invention is described. In the description of thethird preferred embodiment, the same numerical references are attachedto the same components as the first and second preferred embodiments andtheir description of the same functions and effects as the first andsecond preferred embodiments are omitted.

FIG. 11 shows the conceptual block configuration of the poor recordingdetection device in the third preferred embodiment. FIG. 12 is thedetailed block diagram of the image correction unit 10 in the poorrecording detection device in the third preferred embodiment.

The third preferred embodiment shown in FIG. 11 is characterized in nothaving the calibration process as shown in FIGS. 1 and 7 and correctingin real time when normally recording. As to its means, the switch (SW01)shown in FIG. 11 always selects the input recording data 2 to input itto the image correction unit 10 and the input recording imageinformation obtained by detecting the input recording image 3 b which isobtained by recording the input recording data 2 on the recording medium3, by the camera unit 4 is always connected to both the image correctionunit 10 and the poor recording determination unit 11 by a switch (SW02).

By such a connection, since detection is performed at the state wherecorrection information is always added to the input recording data 2, bythe poor recording determination unit 11, as shown in FIG. 12, there isno need to switch between calibration and normal recording operationstimewise, and the print position deviation and gradation error initiallyowned by the image recording apparatus are corrected by a specific timeconstant, thereby enabling accurate detection in real time.

At this time, for a method for detecting without being affected by thespatial interference of surrounding dots in order to extract the nozzleposition and gradation information from the input recording data 2 asthe reference recording data, area division by a threshold process andfeature amount extraction by a template method can be used. Hereinafter,they are described with reference to FIGS. 13 and 14.

For example, in the case where the white-level gradation of 255 of theRGB 24-bit input recording data is corrected, in S11 shown in FIG. 14the input recording data is one piece after another, for example, byconverting dots of 250 or more and those of less than 250 into 255 and0, respectively, with 250 as its threshold and in step S12 a white andblack intermediate image in two gradation as shown in FIG. 13 istemporarily generated. It is because the probability of extracting dotswhich become the reference recording data in the allowable range of agradation correction error is improved that the threshold is 250 insteadof 255.

Then, in step S13, the intermediate image is collated, for example,using a 3×3 template with 3 dots in each of the main and sub scanningdirections. For this template, a pattern in which a gradation value of255 is inputted to all of the 9 dots is used in order to extract whiteportions as shown in FIG. 13A.

By this, in step S14, a feature amount-extracted image composed of dotareas with the amount of feature in which all the 3×3 dot areas are 255gradation can be obtained. A dot extracted as the reference recordingdata used for gradation correction in this obtained white dot area canprevent correction accuracy from deteriorating due to ink blur fromsurrounding dots, the interference of adjacent dots due to theresolution shortage of a camera system and the like by making it onecenter dot.

After the input recording data before extraction is recorded on therecording medium 3, the linearly-arrayed correction information shown inFIG. 4D can be obtained by comparing the dots of the featureamount-extracted image thus obtained with dots matched with thepacked-up input recording information in the main scanning direction andpoor recording is detected one after another by transmitting thecorrected input data gradation-corrected by this to the poor recordingdetermination unit 11.

Although immediately after correction, correction information being alinear array is only dispersedly embedded, by repeating the process oneafter another at the almost the same speed as carrier speed, the numberof arrays in which correction information is embedded can be increasedand the number of gradation-corrected dots increases as time elapses.Thus, poor recording is detected during its actual operation whilegradation is corrected.

In the case where black-level gradation of 0 of the input recording datais corrected, in step shown in FIG. 14 the input recording data isdigitalized one piece after another, for example, by converting dots of5 or more and those of less than 5 into 255 and 0, respectively, with 5as its threshold a white and black intermediate image in two gradationas shown in FIG. 13 is temporarily generated.

After that, the process is performed in the same procedure as thewhite-level gradation correction. However, for the template, a patternin which 0 is inputted to all of the 9 dots is used in order to extractblack portions as shown in FIG. 13B.

Furthermore, a plurality of intermediate gradation levels can beextracted in the same procedure by making the threshold and a gradationvalue inputted to the template intermediate gradation, therebycorrecting a non-linear gradation characteristic.

Next, the case of correcting the nozzle position of the recording headis described. It flowchart is the same as that of gradation correctionshown in FIG. 14. A dot pattern to be extracted from the input recordingdata as the reference recording data is one whose gradation close toblack as much as possible and whose width is one dot, as shown by 25 inFIG. 6B since it requires position information in units of one nozzle.Since its width is one dot and thin and it is easily affected by theresolution of the camera system, position correction errors can bereduced if two thresholds are set and is three-valued when dividing thearea by the threshold. Therefore, it is effective.

In the example shown in FIG. 13, in step 11 the three-valued thresholdis set to 128 and 250. Thus, the input recording data is three-valuedone after another by replacing dots with gradation values of 250 ormore, dots of 128 or more to less than 250 and dots less than 128 withthose of 255, 128 and 0, respectively, and in step S12 an intermediateimage in three gradation is temporarily generated.

Then, although in step S13 the intermediate image is collated using a3×3 template of 3 dots as in the gradation correction, in this case thepattern shown in FIG. 13C, in which 0 for extracting black and 255 forextracting white are inputted and arrayed in the center of the mainscanning direction and at its each end, is used. By using this pattern,correction accuracy can be prevented from deteriorating due to ink blurfrom surrounding dots, the interference of adjacent dots due to theresolution shortage of the camera system and the like.

In order to eliminate dots in 128 gradation between white and black, setin the three-valuing, it is designed that only gradation values of 0 and255 are inputted to the pattern. Although the extraction ratio obtainedwhen using this pattern sometimes low depending on the contents of theinput recording data, in that case the patterns shown in FIGS. D, E andF can be also prepared in advance, and can be also used accordingdepending ob the extraction ratio.

As in the gradation correction, after the input recording data beforeextraction is recorded on the recording medium 3, the linearly-arrayedcorrection information shown in FIG. 4D can be obtained by comparing thedots of the feature amount-extracted image obtained thus with dotsmatched with the packed-up input recording information in the mainscanning direction and poor recording is detected one after another bytransmitting the corrected input data gradation-corrected by this to thepoor recording determination unit 11.

As described above, according to the third preferred embodiment, thereis no need to switch between calibration and normal recording operationstimewise, and the print position deviation and gradation error initiallyowned by the image recording apparatus are corrected by a specific timeconstant, thereby enabling accurate detection in real time.

Although each of the preferred embodiments of the present invention hasbeen described so far, the present invention is not limited to theabove-described preferred embodiments and can be variously improved andmodified as long as the subject matter of the present invention is notdeviated. For example, some components can be deleted from the entireconfiguration shown in each of the above-described of the presentinvention. Furthermore, the different components of each of thepreferred embodiments can be also combined appropriately.

The factor of the items correctable by the image correction unit in eachof the above-described preferred embodiments is not limited to eachnozzle space of the recording head and also includes a skew factor dueto the rotation deviation of the entire head and the position deviationof the carrier unit. The correctable gradation characteristic alsoincludes a white level, a black level, a gamma characteristic, colorgradation in colored image and the like.

In each of the above-described preferred embodiments, for the recordingmedium, a pre-printed medium whose background is printed, a coloredmedium and a medium with holes can be also used. Since the referencedetection information including an image on the recording medium beforerecording and the input recording data are related by the calibrationoperation in the image correction unit 10, poor recording can bedetected as in a normal white recording medium. If the correction of abi-dimensional image on the medium with background and holes and thelike must be corrected, bi-dimensionally arrayed correction informationis used. Poor recording due to the color difference, partialmissing/dirt of the recording medium can be detected simultaneously.

Furthermore, as a means for separating poor recorded image itself fromthat due to the partial missing/dirt of the recording medium, two piecesof correction information memory can be also provided for the imagecorrection unit 10. As to the procedure, firstly, inputting andrecording white paper information to and on the reference recording datain the calibrating operation and comparing the detected referencedetection information with the reference recording data of white paper,correction information only about the recording medium itself isobtained and is stored in the correction information memory forrecording medium itself.

Then, correction information also including the correction informationabout the recording medium itself can be obtained by recording theabove-described normal reference recording data and then corrected inputrecording data also including the correction information about therecording medium itself can be obtained. Furthermore, corrected inputrecording data only about the recording medium itself can be obtained bydeducting the already detected recording medium itself from thecorrected input recording data including the correction informationabout recording medium itself. The poor recorded image itself and poorrecording due to a poor recording medium can be individually detected bychecking twice using these two pieces of corrected input recording data.

The printing method is not limited to an ink-jet method and it issufficient to be recorded in units of dots. A printer using anelectrostatic or thermal printing recording head can be also used. Thepresent invention can be also applied to a printer for offset print,perforated plate print or the like.

According to the present invention, a poor recording detection devicefor accurately detecting poor recording without being affected byprinting position deviation and a gradation error initially owned by aprinter and an image recording apparatus using it can be provided.

1. A poor recording detection device for forming dots on a recordingmedium on the basis of input recording data by a recording head anddetecting poor recording when recording, comprising: an illuminationunit which applies illumination light to the recording medium after therecording; a camera unit which shoots and picks up an image recorded onthe recording medium to which the illumination light is applied by theillumination unit and which outputs detected information; and a poorrecording determination unit which outputs reference detectioninformation obtained by detecting a reference recording image by thecamera unit after inputting reference recording data as input recordingdata and recording the input recording data on the recording medium asthe reference recording image, generates correction information bycomparing the reference detection information with the referencerecording data and generating corrected input recording data obtained bycorrecting the input recording data on the basis of the correctioninformation, and determines whether the poor recording has occurred onthe basis of a comparison result between the input recording imageinformation obtained by the detecting by the camera unit and thecorrected input recording data after recording the input recording dataon the recording medium as an input recording image.
 2. The poorrecording detection device according to claim 1, wherein the correctioninformation comprises position correction information of a dot in atleast one of a main direction and a sub scanning directions.
 3. The poorrecording detection device according to claim 1, wherein the correctioninformation comprises gradation correction information of a dot.
 4. Thepoor recording detection device according to claim 1, wherein thereference recording data comprises dedicated data different from theinput recording data.
 5. A poor recording detection device for formingdots on a recording medium on the basis of input recording data by arecording head and detecting poor recording when recording, comprising:an illumination unit which applies illumination light to the recordingmedium after the recording; a camera unit which shoots and picks up animage recorded on the recording medium to which the illumination lightis applied by the illumination unit and which outputs detectedinformation; and a poor recording determination unit which outputs inputrecording image information obtained by detecting an input recordingimage recording image by the camera unit after recording input recordingdata on the recording medium as an input recording image information,generates correction information by comparing the input recording imageinformation with the input recording data and generating corrected inputrecording data obtained by correcting the input recording data on thebasis of the correction information, and determines whether the poorrecording has occurred on the basis of a comparison result between theinput recording image information obtained by the detecting by thecamera unit and the corrected input recording data, wherein thecorrection information generation and the poor recording determinationare performed with respect to a same input recording image.
 6. The poorrecording detection device according to claim 5, wherein the correctioninformation is generated by extracting a feature image from the inputrecording image.
 7. A poor recording detection device for forming dotson a recording medium on the basis of input recording data by arecording head and detecting poor recording when recording, comprising:an illumination unit which applies illumination light to the recordingmedium after the recording; and a camera unit which shoots and picks upan image recorded on the recording medium to which the illuminationlight is applied by the illumination unit and which outputs detectedinformation, wherein input recording image information obtained bydetecting an input recording image recording image by the camera unitafter input recording data is recorded on the recording medium as aninput recording image, correction information is generated by comparingthe input recording image information with the input recording data andcorrected input recording data obtained by correcting the inputrecording data on the basis of the correction information, and adetermination is made whether the poor recording has occurred on thebasis of a comparison result between the input recording imageinformation obtained by the detecting by the camera unit and thecorrected input recording data, wherein the correction informationgeneration and the poor recording determination are performed withrespect to a same input recording image.
 8. An image recording apparatusprovided with a poor recording determination device for forming dots ona recording medium on the basis of input recording data by a recordinghead and detecting poor recording when recording, the poor recordingdetermination device comprising: an illumination unit which appliesillumination light to the recording medium after the recording; a cameraunit which shoots and picks up an image recorded on the recording mediumto which the illumination light is applied by the illumination unit andwhich outputs detected information; and a poor recording determinationunit or outputting which outputs reference detection informationobtained by detecting a reference recording image by the camera unitafter inputting reference recording data as input recording data andrecording the input recording data on the recording medium as areference recording image, generates correction information by comparingthe reference detection information with the reference recording dataand generating corrected input recording data obtained by correcting theinput recording data on the basis of the correction information, anddetermines whether the poor recording has occurred on the basis of acomparison result between the input recording image information obtainedby the detecting by the camera unit and the corrected input recordingdata after recording the input recording data on the recording medium asan input recording image.
 9. An image recording apparatus provided witha poor recording determination device for forming dots on a recordingmedium on the basis of input recording data by a recording head anddetecting poor recording when recording, the poor recordingdetermination device comprising: an illumination unit which appliesillumination light to the recording medium after the recording; a cameraunit which shoots and picks up an image recorded on the recording mediumto which the illumination light is applied by the illumination unit andwhich outputs detected information; and a poor recording determinationunit which outputs input recording image information obtained bydetecting an input recording image by the camera unit after recordingthe input recording data on the recording medium as an input recordingimage, generates correction information by comparing the input recordingimage information with the input recording data and generating correctedinput recording data obtained by correcting the input recording data onthe basis of the correction information, and determines whether the poorrecording has occurred on the basis of a comparison result between theinput recording image information obtained by the detecting by thecamera unit and the corrected input recording data, wherein thecorrection information generation and the poor recording determinationare performed with respect to a same input recording image.
 10. An imagerecording apparatus provided with a poor recording determination devicefor forming dots on a recording medium on the basis of input recordingdata by a recording head and detecting poor recording when recording,the poor recording determination device comprising: an illumination unitwhich applies illumination light to the recording medium after therecording; a camera unit which shoots and picks up an image recorded onthe recording medium to which the illumination light is applied by theillumination unit and which outputs detected information; and a poorrecording determination unit which outputs reference recording imageinformation obtained by detecting a reference recording image by thecamera unit after inputting the reference recording data as inputrecording data and recording the input recording data on the recordingmedium as a reference recording image, generates correction informationby comparing the reference detection information with the referencerecording data and generating corrected input recording data obtained bycorrecting the input recording data on the basis of the correctioninformation, and determines whether the poor recording has occurred onthe basis of a comparison result between the input recording imageinformation obtained by the detecting by the camera unit and thecorrected input recording data, wherein the reference recording image isdetected by the camera unit with a higher density than a dot density ofthe recording head and the correction information can be obtainedaccording to brightness information of each pixel.
 11. A poor recordingdetection device for forming dots on a recording medium on the basis ofinput recording data by a recording head and detecting poor recordingwhen recording, comprising: an illumination unit which appliesillumination light to the recording medium after the recording; a cameraunit which shoots and picks up an image recorded on the recording mediumto which the illumination light is applied by the illumination unit andwhich outputs detected information; and a poor recording determinationunit which outputs reference detection information obtained by detectinga reference recording image by the camera unit after inputting referencerecording data as input recording data and recording the input recordingdata on the recording medium as a reference recording image, generatescorrection information by comparing the reference detection informationwith the reference recording data and generating corrected inputrecording image information obtained by correcting the input recordingdata obtained by the detecting by the camera unit on the basis of thecorrection information after recording the input recording data on therecording medium as an input recording image, and determines whether thepoor recording has occurred on the basis of a comparison result betweenthe corrected input recording image information obtained by thedetecting by the camera unit and the corrected input recording dataafter recording the input recording data on the recording medium as aninput recording image.